Recording



Nov. 11, 1952 A. WOLF 2,617,947

RECORDING Filed March 28, 1947 COUNTER 52 AMPL/F/ER 24 a/ FIG. 3.

' INVENTOR. ALEXANDER WOLF A T TORNE Y Patented Nov. 11, 1952 RECORDINGAlexander Wolf, Houston,

Texas Company, tion of Delaware Tex., assignor to The New York, N. Y., acorpora- Application March 28, 1947, Serial No. 737,918

4 Claims.

This invention relates to an instrument for recording the duration of anevent together with the time at which the event takes or has takenplace. More particularly the invention relates to an instrument for thedetermination and recordation of the intensity of radioactivity asdetected by conventional radioactivity detectors.

Radioactivity is conveniently detected by means of gamma ray detectors.Gamma ray intensities may be measured by means of an ionization chambertype of counting instrument in which a current flow is inducedproportional in magnitude to the primary ionization produced in thechamber by incident gamma rays. There are other types of instrumentswell known in the art for the measurement of radiation which are basedon the count of the individual incident rays. In such instrumentsprimary ionization produced in a gas filled chamber by an incident gammaray initiates a large transitory electrical discharge. These dischargesare amplified and counted and the count observed per unit time isproportional to the frequency of the incident rays.

Such detecting instruments do not deliver continuous current but rathera series of sharp current pulses at an average rate which depends on theintensity of the radioactivity to which the detector is exposed. If theintensity of radioactivity varies with time, as is frequently the case,it is desirable to obtain a continuous record of this intensity. Thishas been accomplished in prior practice by recording each individualpulse as a mark on a strip. The interpretation of such a record istedious, because it requires the counting of the number of pulsesproduced during successive time intervals. It has been proposed toreduce the labor involved in counting these pulses by employing a scalecircuit which automatically counts a predetermined number of pulses andin turn produces only one pulse for the above predetermined number ofpulses. However, even with this scale circuit, the interpretation of arecord cannot be made at a glance.

An additional proposal for obtaining a continuous record from theindividual pulses of a radiation detector involves an integrationcircuit, which as the name implies, integrates the pulses and therebyproduces a continuous voltage, the magnitude of which is approximatelyproportional to the number of pulses received during some predeterminedprevious time interval. The inherent diificulty with this type ofcircuit arises from the fact that the output voltage depends on thecharacteristics of the various vacuum tubes employed in the circuit.When an instrument of this type operates for relatively long periods,the

2 aging of the vacuum tubes results in gradual changes in theircharacteristics which in turn results in a drift in' the readingsobtained with a given intensity of radioactivity. So calibrationdifficulties arise.

The instant invention (although applicable generally to the recording ofthe duration of an event together with the time at which the eventoccurred) is concerned primarily with measurement and recording ofvariations in the intensity of radioactivity with time while avoidingthe difficulties outlined above. The invention provides apparatus thatis not susceptible to drift and which does not require frequentcalibration. It permits the elimination of an integration circuit, andin its preferred form permits power line frequency to be employed as itsprimary reference standard. In modern operations, such frequency ismaintained extraordinarily constant.

Basically, the invention contemplates a chart traveling responsive totime, a marker (hereinafter called a pen) mounted adjacent the face ofthe chart and driven transversely to the chart at a greater rate oflinear velocity than the chart, means for initiating the movement of thepen transversely to the chart responsive to the commencement of a givenevent, means for stopping the movement of the pen responsive to thecompletion of the event and automatic means for returning the pen to itsstarting position.

As employed in the measurment of radio activity the apparatus of theinvention comprises the chart and pen, together with electrical means inassociation with a detector of radioactivty, the electrical means beingadapted to deliver an output voltage only after activation by a fixednumber of pulses from the detector, means for initi-. ating thetransverse movement of the pen simultaneously with the commencement ofthe activation of the electrical means, means for stopping the movementof the pen responsive to the appearance of the output voltage from theelectrical means, means for returning the pen to its original positionand means responsive to the return of the pen to its original positionfor resetting the electrical means so that the output voltage will againappear only after activation of the electrical means by a like number ofpulses from the detector.

The invention may be more readily understood from the following detaileddescription taken in conjunction with the accompanying drawing in which:

Fig. 1 is a schematic diagram of one recording apparatus of theinvention;

Fig. 2 is a. diagrammatic representation of-the circuit employed withthe recording means of Fig. 1, for the purposes of measuring andrecording radio activity; and

Fig. 3 is a modified form of the recording means of Fig. 1, adapted tobe operated in conjunction with the circuit of Fig. 2, and to recordonly the maxima .ofthe observed intensity.

The recording mechanism shown in Fig. 1, comprises a chart ll! mountedon suitable rollers 12, I3 which are driven in conventional manner tocause the chart I to move at a constant speed.

The mechanism has a synchronousmotor 16 which is connected to apower'line is-and'runs continuously during operation. The motor turns ashaft l9, which is coupled at its rightxhand end to a clutcharrangement. This comprises a first magnetic clutch 30 mounted directlyon the end of the motor shaft and connected directly to acoaxial:extension'ishaft' 29, and'a second magnetic clutch :3l disposedparallel to the 'firston a jack shaft BS'Aan'd driving acoaxialisub-shaft 35B. A rigidlyzmountedqgear 33' on the motor shaft 19meshes with a gear 35 rigidly mounted on the jackshaft and thus drivesthe second clutch. Thisin turndrivesagear39 on the'sub-shaft 35Ban'd,"-meshing' with a gear 3' 1 rigidly mounted on the extension shaftz'mtransmits ,power to the latter.

"The clutch arrangement permits the shaft 25 to. beturned :eitherclockwise orcounter-clockwise, depending'upon which of its two clutches:is engaged'it-being apparent of course, that only che-clutch'shouldFbeengaged at one time.

The-shaft 25 carries a rigidly mounted worm at its "right hand end. Theworm meshes with a'sprocket 22rotatableon an axis perpendicular to thoseofithezrotatablejparts thus far described and turning 'avcoaxialpinion:24 that engages a rack :261-and movesit to-theright or left, asviewed inzFig. :Ldepending'upon the direction of rota- .tion of theshaft 29 upon which the worm is mounted.

The rack has ra'longitudinal extension arm 21 having a pm 28 on itsrighthand end in engagement with the chart and adapted to move tow'theright" or left thereon under the impetus ofthe'linkages'thus fardescribed.

A limit switch 44 is disposed to the left of the I rack 2.5 and in thepath thereof, so that it is operated when the rack moves sufiicientlyfar .in'its direction, 1. 1e. to the point of engagement'Wlth'LltSYbIIttOD. 45.

- .The functioning :of the .limit switch 44 withrespect.tcitherrecordingapparatus is more clearly described withrelation to Fig. .2, which is-a 'diagramxof :the circuit employed tooperate the recorder of Fig.1 and includes apparatus :neces- "saryzfor"the-determination and recording of radioactivity. Referring to Fig. 2,acounter 51] (which 'may be .anyiconven'tional apparatus for thedetection of radioactivity such, for example,.asfthosecalready.mentioned) is connected to and operates-an amplifier.52 which may include the necessary 'quench circuit, pulse equalizer,etc., devices which are familiar'in the art. Such'cir- "cuitsinamplifiers have'been 'described'in detail in the literature, forinstance in, .Procedures in-Experimental Physics, by John Strong,published by:Prentice Hall -Inc., N. Y. The output .ofthe .amplifierf52is'fed to-a scale circuit'54 of conventional type, for example thatdescribed on page 288 ofthe aforementioned text by Strong. The scalecircuit consistsof aseries of flip flop trigger .circuitssoarrangedthat. a predetermined 4 number of pulses have to be fed into the inputside of the scale circuit before a voltage appears across outputterminals 55 and 5B. The number of pulses which must be fed into theinput of the scale circuit before a voltage appears across the outputterminal depends upon the number of .stages built into the .scalecircuit. Ordinarily this number is a power oil such as 2, 4, 8, 16, 256,512, 1024, 2048, etc. After the predetermined number of pulses have beenfed to the input of the scale circuit, and the voltage has appearedacross its output terminals, the circuitcan beso arranged that currentwill continue to flow in the output circuit until the entire scalecircuit or a portion of it is de-energized or freset. Thisdeenergizaticnis accomplished by breaking a contact if! in a circuit between twoexternal terminals 58, 59. These terminals are for the purposes ofdescription termed reset :switch terminals. When .the "reset switchcontact flil is actuated, the scale tcircu'it will'proceed again withits operation until the same number of pulses is fed into theinput, atwhich time the voltage will appear across the output terminals 55 and 55"and current "will flow through'the output circuit Bil until suchtime asthe reset switchis again operated.

Theclutches Sit-and 3! are controlled by the scale circuit 54 throughrelays'BZ, B3,- Maud the limit switch ili' connected in the output ofthecircuit. These relays are operatedon the one hand by the limit switch'lfil whenever itis actuated by'the rack 25 'as described with referenceto Fig. l, and on the other hand bythe appearance of the output voltageon the scale circuit 5 3. In the operation of the circuit of Fig/2.which is'cyclic innaturean'd thuscontinuous, a switch arm G5A'of thelimit switch l i is thrown in contact with a Jterminal'BEA'When the rack2e presses on the switch plunger "as described with reference to Fig.1..It is thrown .into'contact with another terminal 55 after the rack'hasstarted traveling toward'the right *and hasreleased .thebutton 45. 7

Since the'operation of the apparatus iscyclic and thus continuouaforthepurposes of description'it is most convenient to start at anarbitrary period in the operational cycle and proceed through the entirecycle until the original condition has been achieved. For purposes ofthis description, it may be assumed that at one particular period in thecycle the limit'switch 44 is in contact with the terminal .55 whichthereby connects the irelayfifi'with the power inputline BIthroughalocking contact 66 while relays 82 and fidware open. At thisstage of the cycle, a solenoid operation coilSilAiof .the clutch 30)connected across the 'open :relay 82 is not energized, and the resetterminals 58 and 59 connected across the'relay B2 are open so'thatthe'scale circuit 54 is inoperative. A solenoid operation coil 31A of theclutch 3| is connected across the relay fieand at thisstageis closed,Consequently, the pen 28 shownin Fig. l is pulled tothe left by means ofthe rack.25.

When the rack strikes the limitswitch button 5, the switch arm 45Ais'thrown into contact with the terminal 65A, whereupon'the relay 63 isopened andthe'relay'GZ is closed and-is locked in the closed position'bylocking contacts 58, 59, the contact 69 being closed-when the relay'64 is open. -Asaconsequence-of opening the relay 63, the clutch 3| is.de-energized so that the pen .23.stops travelingto-the left. As aconseguence of .closing .the .relay .52, the -reset terminals; 58. 56.are; closed. through. the. contact. 10, so thatthe-scale circuit starts.operating. At the same: time the clutch 30.: is-energizedi by the relay61 through; the: contact 1.1 so that theworm. 21, shown in 1,is1rotated; in. the opposite direction; causingzthe pen. to. travelacross the chart away fromthe: limit switch. As soonv as the; rack 26:-releases; the; buttonof. the limit. switch: 44,. the switclharm 45Adrops back to.) contact the. terminal. 6,5. This hasrno immediateeffect. inasmuch as the: relay 62: is locked in. the closed position bythe contacts 68, 69, asalreadydescribed.

The: travel of the: pen 28 across the chart [0 in. they right hand;direction will continue until the; counter- 56.; has: delivered. the.required. numher. of pulses: to; the. scale; circuit: 54.. When thishappens a: voltage will: appear. across the output terminals: 55..5.61,. and this will. energizemhe relay 64 through the circuit 60. Whenthe relay 64 is. energized thecontact. 69- is opened, thereby opening,the. relay 62, whereupon the contact 14 is: closed-dov energize therelay 63.. As a; consequence of the opening; of the relay 62,. theclutch 30. is released and the penstops moving to the right; At the,same time the contact 7-0 of the relay 62. is opened and therebyde-energizesthe scale circuit which: in turn opens the relay 64.

Simultaneously with the de-energization of relay 64,. relay 6-3is-closed and; locked in the closed position through the contact andtherefore remains. closed: even after the de-energization of the relay64..

The closing of the contact 15; by the energization of the relay 63,actuates the clutch 3| so that the pen startsv moving to the left andthe apparatus.- has returned to the original condition.

The foregoing operation. will. continue. to repeat itself indefinitelyand the pen. 28 will trace the saw toothed curve shown. on the. chart Inin Fig. 1,.theamplitude oi'the. curve being a measme of the intensity ofthe radioactivity.

Toinsure proper operation, the relays should, of course, be adjustedproperly with respect to each other. Thus relays 62 and 63shouldoperate. almost simultaneously and the release time of they relay64- should be greater than the closing tim of relay 63 in. order topermit the closing of the relay 63 prior to the de-energization of relay6.4;

In furtherexplanation, the" function of the contact 69 is to break thepower supply circuit to the coil of the relay 62 at the instant whenthe: scale circuit has reached a predetermined value. and has producedcurrent through the winding of the. relay 64 This: opens the contact 69and deenergizes the relay 62;. which in turn deenergizes the clutch byopening the contact 1| of the relay 62'. When this occurs the travel ofthe pen 23- toward the right is stopped. Simultaneously the opening ofthe relay. 62 breaks the: contact at 16' and thereby deenergizes thescale circuit. This cuts on" the current to the. coil. of relay 64' andallows it to drop. open. Actually the relay 64 is operatedonlymomentari-ly. However, during this period of momentary operation ofthe relay 64, the contact 14 is closed-thereby supplying power to thecoil of the relay 63. Such a supply of power causes the relay 63 tooperate and to close the contact 66 providing an auxiliary pathindependent of the contact 14 by which the relay 63 may be maintained inan energized condition, i. e. locked, so that it will not fall open whenthe relay 64- fal1s open on deenergization or the soalecircuitl The. cloing or the. relay 63 also and thereby operated it. a

suppliesv P wer; to the clutch 31. through the con.- tact. 1.5-and thusstarts the, pen in its travel to.- ward the left. To summarize. it mightbe said that the. contact. 69. is the unlocking; contact for the relay62- while the contact. 68. is the locking contact for the relay 62. Thecontact- 66 is the locking contact for the; relay 63-. The. function ofthe relay 64, among other-s is. to reverse the: travel. of the; penfrom; right to left-and the function of the limit. switch, 4.4v istoreverse; the travel: of the, pen from left. to right. Itshould be.noted that the relays 62,. 63 have a locking contact and; an unlockingcontact. The locking contact for the relay 62. is the, contact 68.. Theunlocking contact for the relay 62 is. the contact 69; The,lockingcontact for the relay 6.3 i the contact 66 and the unlockingcontact for. therelay 63 is thecontact' 65.

In many applications the intensity of radioactivity varies byonly a.small fraction of its average value. In such caseit become desirable to.record only a small part of the motion of the rack 26. This isaccomplished by a modification of the apparatus illustrated in Fig. 3.

In: Fig. 3, which is a partial view of a modification: of the apparatusof Fig. 1, the pen 28 is mounted on a. carriage 86 which travelstransversely tothe: chart l6 along parallel guide rods 8|, 82. A rack 84generally similar to the rack 26 of. the apparatus of" Fig. 1, isprovided and differs from. the other rack only in increased length. Thelimit switch 44 is the same as the limit switch 44 in Fig. 1, but isplaced farther to the left of the rack 84 than in the other embodiment.When the rack 84 is in its extreme left hand position, the pen carriageis brought against stops 86, 81 on the guide rods 8|, 82 by means ofaweight 88 connected thereto by a cable 89 which travels over a pulley90. The cable 89 is affixeci to the carriage 86 by a hook 92. (Movementof the carriage toward the left may be accomplished by a spring or othermeans which will performv the same function as the weight 88.)

The rack 84 (which is reciprocated in the same manner as that of Fig. 1)engages the p riage 8U Somewhere in the mid stroke of the rack so thatonly a portion of its travel is actually recorded. By this means it isunnecessary to have a chart as wide as the full travel of the rack.

It is also within the contemplation of the invention to employ acircular chart instead of the ribbon type illustrated. Such a circularchart can be readily adapted to the recording apparatus of the presentinvention by providing a linkagebetween the pen and the rack of a typewhich permits the pen to pursue a proper course on the circular chart.

To summarize the operation of the apparatus of the invention, theaverage frequency of the pulses from the counter 56 depends on theintensity of the radioactivity being measured (say the gamma radiationsencountered along a well bore), and therefore the time required for thescale circuit to trip, i. e., for a voltage to appear across the outputterminals 55, 56, likewise depends on this intensity. The higher theintensity, the shorter the time which will elapse between the reclosingof the the terminals 58 and 59 and the tripping of the scaIe circuitoutput. It is this time which is measured and recorded by the recordingdevice gear' 22 attach d. tothe pinion '24, 'which in turn tranverseagain energized.

drives the rack 26 (or the rack 84 as shown in Fig. 3). Thus, when theclutch 30 is energized operating and before the output voltage appearsacross the terminals 55, 5 6. Thus the rack 26 will travel to the rightuntil this output voltage appears across the output terminals of thescale circuit 54 and the length of the lines formed on the chart are ameasure of the time required for this output voltage to appear, thistime being inversely proportional to the intensity of the radiationregistering on the counter 50. Hence the length of the linedrawn'on thechart l0 will be inversely proportional to the intensity of theradiation.

When the output voltage does appear across the terminals 55 and 56 ofthe scale circuit 54, the clutch 30 is de-energized (i. e. released) andthe clutch 3! is energized (i. e. engaged) causing the'rack 25 to traveltoward the left instead of toward the right. When the rack 28 reachesthe left hand extremity of the permissible travel it operates the limitswitch 44, releases the clutch 3i and engages the clutch 39 at the sametime resetting the scale circuit so that it will again receive apredetermined number of pulses from the counter 50 prior to theappearance of a voltage across the output terminals 55 and 56.

The time required will be proportional to the intensity of the radiationbeing received at that particular time by the counter 50.

It is apparent that by means of the apparatus of the invention one mayobtain a continuous picture of the intensity of radiation at any giventime and by drawing a curve through the maximum points on the graphformed on the chart I9, may obtain a picture of the fluctuation in theintensity with time.

The apparatus described is applicable to the determination of theduration and the time of any given event and is not restricted to usefor the determination of the intensity of radioactivity; In thisadditional capacity, the apparatus of the invention becomes in effect anoperation time recorder. Conventional instruments for accomplishing thissame function efiect the measurement of the time duration along thelongitudinal axis of a chart and for this reason are limited in theirapplication. They are not capable, practically, of measuring times whichare very short, say one minute or less, because of the excessive chartspeeds which would be required.

The instrument'of present invention is particularly adapted to measuringthe duration of the operation of a device Where such duration is short,say a minute or less, since it utilizes the dimensions of the chart forrecording the duration of an operation and the longitudinal dimensionsthereof only for recording when the operation is performed.

For employing the recorder of the invention for this last named purpose,the circuit shown in Fig. 2 need only to be modified so that the clutch30 will be energized while the device in question is operating and theclutch 3! will be energized when the operation of the device hasterminated, so as to return the pen 28 back to the original startingposition-where it is ready to register another operation whenever theclutch 30 is i Many modifications in the apparatus of the invention mayoccur'to those skilled in the art.

flfhusthe gear train operated by. the synchronous motor It may be'sodesigned that'the movement of the pen to the left is more rapid than themovement to the right, making it possible to utilize a greater portionof the total time for the actual measurement. Similarly the two clutchesmay be replaced by other means for alternately rotating the shaft 20 inone direction or another. Thus, the starting, stopping and reversing ofthe shaft can readily be accomplished by mcansc'f two brakes. Such asystem has been used in the conventional differential transmission ofolder model automobiles.

It may be desirable to include an additional limit switch to prevent theovertravel of the pen 28 to the right. Such a switch can be' employedeither to stop the mechanism entirely or to apply a voltage across theoutput terminals of the scale circuit which would automatically reversethe motion of the pen. 5

The scale circuit need not include the excessive number of stagesrequired for the large number of pulseswhich one might wish to count insome cases. It is within the contemplation of the in- .vention toconnect the output of such a scale circuit to a mechanical'pulse counterand to employ an electrical contact attached to the pointer of themechanical counter to operate the relay 6d at the end of one revolutionof the pointer. In this fashion, the scale circuit may be employed toregister an output voltage after say 256 counts, thereby move amechanical counter one point. In short, the scaling of the circuit maybe magnified by the incorporation of such a mechanical counter.

By addition of a pair of contacts to the relay 63, a stepping relay maybe operated at the end of each right hand stroke of the pen 28. Thisstepping relay may be used to switch the input .of the scale circuit orthe input of the amplifier to a whole series of counters in succession.This makes possible measurement at a number of points with the samerecording instrument; 'Of course, each maximum point on the curve wouldthen refer to a difierent point of measurement-in succession. Theparticular counter on which measurement is made can readily beidentified, for instance, by the addition of a second pen connectedmechanically to the stepping .relay which would register on the chart amark corresponding to the position of the stepping relay and therebyidentify the counter from which a particular measurement comes. Similarmechanisms for recording a plurality of different measurements are foundin use in temperature recording and the like, and meansfor indicat mgwhich particular quantity is being recorded at any given interval isfamiliar to those skilled inthe art. l

In an alternative embodiment, the apparatus of the invention may be soconstructed that a separate recording element is associated with eachcounter, a common scale circuit and relay system being employed for all.In this embodiment the recording pen pertaining to any courtter isinactive when measurements are being made on the other counter.

I claim:

I. An apparatus for recording the intensity of radio-activity whichcomprises a chart, means for driving thechart at a constant speed, apen, means for moving thep'en transversely to the chart, a detector forthe radio-activity, electrical means in association with the detectordelivering after setting an output voltag lonly'after activation by afixed number-of pulses fromthe detector, means for initiating themovement of the of said output voltage, means for returning the pensimultaneously with the starting of said elecpen to its originalposition and means responsive trical means, means for stopping themovement to the return of the pen to its original position of the penresponsive to the delivery of output to reset said electrical means sothat said output voltage by the electrical means, means for revoltagewill again appear only after activation turning the pen to its originalposition and means of said electrical means by said fixed number ofresponsive to the return of the pen to its original pulses.

position to reset the electrical means so that out- 4. An apparatus forrecording the intensity of put voltage will again appear only afteractivaradio-activity which comprises a chart, means for tion of theelectrical means by the fixed number driving the chart at a constantspeed, a pen, of pulses. means for moving the pen transversely to the 2.An apparatus for continuously recording the chart, a detector for theradio-activity, electrical intensity of radioactivity which comprises achart, means connected with the detector for delivering means fordriving the chart at a constant speed, after setting an output voltageonly after activaa pen movable transversely to the chart, driving tionby a fixed number of pulses from the demeans for moving the pen ineither direction tector, means for initiating the movement of thetransversely to the chart, a detector for the radiop n at a pedetermined time interval after the activity, electrical means connectedto the deinitiation of said electrical means, means for tectordelivering after setting an output voltage stopping the movement of thepen responsive to only after activation by a fixed number of pulses he dl v ry f i Ou pu v l m a s for from the detector, means for engaging thedriving e urning the p n to its Original p s t on a d means with the pensimultaneously with the automatic means operable after the return of theinitiation of said electrical means, means for D 130 its Original postion to reset said electrical disengaging the driving means from the penremeans 50 that Said Output Voltage Will again psponsive to t delivery fsaid utput lt pear only after activation of said electrical means meansconnected with said last named means by Said fixed number o pu ses. forengaging the driving means with the pen so as to return the pen to itsoriginal position, and ALEXANDER WOLF" means responsive to the return ofthe pen to its original position for resetting the electrical meansREFERENCES CITED so that the output voltage will again appear only Thefollowing references are of record in the after activation of theelectrical means by the file of thls P fixged number 0% puflses. d1 th tit f UNITED STATES PATENTS An appara us or recor ng e in ens y oradio-activity which comprises a chart, means $gi ;2 A 3 for driving thechart at a constant speed, a pen, 1 1043D7 McLeag 1914 means for movingthe pen transversely to the 1961170 Robinson g 1934 chart, a detectorfor the radio-activity, an ampli- 2108037 Au Feb 1938 fier connected tothe output of the detector, elec- 2181728 gg- 1939 trical meansconnected with the amplifier for 2390178 Rutherfgrd g 1945 deliveringafter setting an output voltage only 2485730 Gifien et a1 1949 afteractivation by a fixed number of pulses f1 om the detector, means forinitiating the movement REIGN PATENTS oi. the pen simultaneously withthe initiation of Number Country Date said electrical means, means forstopping the 332554 Great Britain October1932

1. AN APPARATUS FOR RECORDING THE INTENSITY OF RADIO-ACTIVITY WHICHCOMPRISES A CHART, MEANS FOR DRIVING THE CHART AT A CONSTANT SPEED, APEN, MEANS FOR MOVING THE PEN TRANSVERSELY TO THE CHART, A DETECTOR FORTHE RADIO-ACTIVITY, ELECTRICAL MEANS IN ASSOCIATION WITH THE DETECTORDELIVERING AFTER SETTING AN OUTPUT VOLTAGE ONLY AFTER ACTIVATION BY AFIXED NUMBER OF PULSES FROM THE DETECTOR, MEANS FOR INITIATING THEMOVEMENT OF THE PEN SIMULTANEOUSLY WITH THE STARTING OF SAID ELECTRICALMEANS, MEANS FOR STOPPING THE MOVEMENT OF THE PEN RESPONSIVE TO THEDELIVERY OF OUTPUT VOLTAGE BY THE ELECTRICAL MEANS, MEANS FOR RETURNINGTHE PEN TO ITS ORIGINAL POSITION AND MEANS RESPONSIVE TO THE RETURN OFTHE PEN TO ITS ORIGINAL POSITION TO RESET THE ELECTRICAL MEANS SO THATOUTPUT VOLTAGE WILL AGAIN APPEAR ONLY AFTER ACTIVATION OF THE ELECTRICALMEANS BY THE FIXED NUMBER OF PULSES.